The present invention concerns a gear drive, especially a planetary gear drive, with a housing and with at least one shaft passing through a housing wall, especially an input and/or an output shaft, a pressure-equalization chamber being provided between the interior of the drive housing and the external atmosphere for equalization of pressure.
Known, for example, from DE 40 18 601 A1 is equalizing the pressure in a gear drive of the type mentioned above with the aid of a disk-shaped membrane secured via the mounting edge in a ventilation opening or pressure-equalization chamber in the housing wall of the drive, the two deformation endpoints of the membrane defining an approximately lens-shaped space.
Known from DE 34 39 225 C2 is a gear drive again with pressure equalization in the housing wall, a membrane-like hollow body shaped approximately like a bellows being positioned in a ventilation opening of the housing wall.
In all of these cases, the housing wall must have sufficient room as regards both the surface area expanse of the corresponding point in the housing wall as well as its thickness.
However, due, for example, to housing designs relating to certain installation conditions or for structural reasons, incorporating such a ventilation opening or damping chamber of sufficient size in a housing wall of the gear drive may not be possible or in many cases only insufficiently so.
Know from DE-GM 1 933 920 is a gear drive of another type, in which ventilation occurs via an output shaft with a longitudinal borehole leading to the outside and a cross borehole leading to the interior of the drive. A pressure-equalization chamber is not provided here so that an exchange of oil vapors or similar impurities can occur between the interior of the gear drive and the external atmosphere during operation.
The problem therefore exists of providing a gear drive of the type mentioned above in which pressure equalization between the interior of the drive housing and the external atmosphere is possible without providing an appropriate pressure-equalization chamber of the size necessary for the pressure equalization in the housing wall.
The solution to the apparently contradictory problem includes providing the ventilation opening or pressure-equalization chamber positioned in at least one of the shafts passing through the drive housing and/or in related drive partsxe2x80x94in the case of only one exiting shaft, in that shaftxe2x80x94and is connected, on the one hand, with the interior of the gear drive and, on the other hand, with the external atmosphere. The solution further includes providing a membrane deformable by pressure differences positioned and mounted in the pressure-equalization chamber.
The invention thus makes use of the fact that in a gear drive as defined above, a shaft passes through the housing wall. The invention then utilizes this shaft in producing pressure equalization between the interior of the housing and the external atmosphere so that corresponding ventilation openings or pressure-compensation chambers can be avoided in the housing wall. If necessary, however, pressure equalization can also be attained through combination of a housing-wall pressure-equalization chamber possibly not sufficiently large all by itself and a further chamber in the shaft and/or a related drive part.
Effective pressure equalization between the interior of the gear drive and the external atmosphere with simultaneous prevention of leakage of lubricant or entrance of impurities can be attained through the fact that the membrane positioned in the pressure-equalization chamber in the interior of the shaft and/or drive part connected directly or as one piece with the shaft is essentially pot- or cap-shaped and exhibits, starting from the circular mounting edge, a circular side wall as well as a bottom wall connected to the side wall at the end opposite the mounting edge. The membrane with the bottom wall can be moved with respect to the mounting edge by turning it inside out. The membrane represents a tight seal between the external atmosphere and the interior of the gear drive so that no dirt can get into the drive from the outside and no lubricants can pass from the interior of the gear drive to the outside. Nevertheless, effective pressure equalization can be attained. Here, the invention makes use of the fact that especially output drive shafts frequently have a large diameter appropriate for transmitting high torques and radial loads and permitting the positioning of a corresponding pressure-equalization chamber in their interior without adversely affecting the actual functioning of the shaft.
With respect to positioning in the interior of a drive shaft and/or a drive part associated therewith, it is useful if the pressure-equalization chamber and the membrane as well as the side wall have an essentially circular cross-section and are particularly positioned concentrically in the interior of the shaft. At the same time, out-of-balance problems are avoided due to the concentric arrangement and the resulting uniform weight distribution.
The bottom wall of the membrane can run approximately parallel to the plane of the mounted edge and can itself be flat or curved. The circular side wall can be of an essentially constant size over the entire axial range. Thus, depending on the size of the pressure differential to be equalized, the bottom wall can be moved back and forth with respect to the mounting edge by turning the side wall partially or entirely inside out.
Here, the inner diameter of the cap-shaped or hat-shaped membrane in the area of the mounting edge can be about the same, possibly smaller, or especially somewhat larger than the axial range of the nondeformed membrane. Especially a membrane in which the axial length of the side wall is less than the diameter can be readily turned inside out. However, this also applies for the case in which the two dimensions are equal or in which the diameter is somewhat shorter than the axial length of the side wall. Particularly also making a contribution here is a relatively large bottom wall, on which the overpressure acts.
The pressure-equalization chamber positioned in the shaft and/or a drive part associated therewith can be dimensioned at least twice as large in the axial direction as the axial length of the nondeformed membrane, and the attachment of the mounting edge of the membrane can be provided at about half the height of the pressure-equalization chamber. This permits inversion of the membrane from a nondeformed position in the opposite direction practically over the entire axial length. A correspondingly large volume is available for pressure equalization. The drive part associated with the shaft can be one piece with the shaft or can be connected via a pressing or screwing process or the like so that the pressure-equalization chamber could also extend over such a point of connection in the interior of the shaft and the drive part.
Starting from the pressure-equalization chamber, a borehole or channel can run through the shaft, especially positioned coaxially in the center of the shaft. As a result, the connection of the pressure-equalization chamber with the external atmosphere can be accomplished in particularly simple fashion in that the shaft itself contains the corresponding connecting channel and leads through the housing wall to the outside. The coaxial arrangement in the shaft is particularly simple to produce and leads to a rotationally symmetric shaft. It would also be conceivable, however, if the space at the end of the shaft is needed for something else, e.g., the attachment of mounting elements or the like, to lead the corresponding ventilation channel somewhat obliquely through the shaft toward the outside and to let it exit not at the shaft end wall, but at a peripheral point on the shaft.
In order to protect the membrane within the pressure-equalization chamber as much as possible from mechanical damage, the pressure-equalization chamber can exhibit on the side opposite the borehole or channel a particularly removable or openable cover plate with a pressure-equalization opening, the plate shielding the pressure-equalization chamber toward the interior of the gear drive. If the pressure increases in the interior of the gear drive, this can spread through the mentioned pressure-equalization opening into the pressure-equalization chamber and lead to appropriate deformation of the membrane and vice versa. Here, air and/or lubricant from the gear drive can enter through the pressure-equalization opening into the pressure-equalization chamber and load the membrane and, upon reverse movement, be forced back into the gear drive.
The membrane can exhibit at the mounting edge a radially outwardly protruding flange for clamping and attachment within the pressure-equalization chamber. This represents an especially effective attachment which, at the same time, leads via clamping of the flange to a good seal.
The cover plate can exhibit protrusions locking into the wall of the pressure-equalization chamber orxe2x80x94especially preferredxe2x80x94a circular peripheral section as a hold-down device for securing the mounting edge of the membrane. As a result, the cover plate obtains a double function in that is shields the membrane from the gear-drive interior and simultaneously secures it in the pressure-equalization chamber.
The pressure-equalization chamber can have a larger cross-section in the area of the cover plate and the hold-down section than in the area into which the membrane can be turned inside out by an increased pressure in the interior of the gear drive, and an offset for accepting the mounting edge or flange of the membrane can be provided between these two areas of the pressure-equalization chamber, the hold-down section of the cover plate being supported in the installed position on the offset. The larger cross-section of the pressure-equalization chamber thus accepts the flange of the membrane serving as mounting edge as well as the hold-down section of the cover plate so that in the finally assembled form, the size of the pressure-equalization chamber within the hold-down section of the cover plate is approximately comparable to that of the chamber over the rest of the range if the radial thickness of the hold-down section corresponds to the radial dimension of the offset.
The circular side wall of the nondeformed membrane can form a truncated cone and attenuate toward the bottom wall at an acute angle. As a result, the tendency of the membrane to turn inside out can be improved already at low pressure differentials.
Especially upon combination of one or more of the above-described features and measures, one obtains a gear drive with pressure equalization between the interior and the external atmosphere without requiring corresponding openings and pressure-equalization chambers in the housing wall of the drive. One or more of the shafts belonging to the gear drive and passing through the housing wall can be used to bring about this pressure equalization, and also connect the pressure-equalization chamber with the external atmosphere via a corresponding borehole running through the shaft or a corresponding channel. Here, no additional space is needed for such pressure equalization if the shaft is designed for transmitting a relative high torque or also for high bending forces and is of an appropriately large size and can transmit these forces provided that the shaft is hollow over part of the length, namely in the area of the pressure-equalization chamber.